inverse trig function help,

Without using a calculator, work out, giving your answer in terms of , the value of;

I know how to work out arcsin and arccos, by looking at the x and y values on the unit circle, but how do I work out acrtan? because the way I understand it is that tan = sin/cos which is equal to y/x.

Without using a calculator, work out, giving your answer in terms of , the value of;

I know how to work out arcsin and arccos, by looking at the x and y values on the unit circle, but how do I work out acrtan? because the way I understand it is that tan = sin/cos which is equal to y/x.